This invention relates to electron beam exposure systems for selectively irradiating workpieces and, more particularly, to a pattern data handling system for providing beam blanking data for an electron beam exposure system.
Electron beam exposure systems have been developed for use in the manufacture of microminiature semiconductor devices. A pattern is produced in a mask or a semiconductor wafer coated with an electron resist material by exposure to an electron beam. In the exposure of a pattern, an electron beam is scanned across the surface of a workpiece positioned perpendicular to the direction of the beam. As the beam is scanned across the surface of the workpiece, it is turned on and off, or blanked, to produce the desired pattern. In order to minimize pattern distortion, the deflection of the electron beam is limited and the workpiece is mechanically positioned under the beam by a moving stage. The electron beam is scanned in the y direction and the stage moves in the x direction so that a stripe of the workpiece is scanned. By additional stage movements, multiple abutting stripes are scanned until the entire workpiece has been scanned. Thus, while the electron beam scanning range may be one millimeter, the moving stage permits exposure of a workpiece several inches square. Such a system is described in U.S. Pat. No. 3,900,737 issued Aug. 19, 1975 to Collier et al.
As might be expected, large quantities of data are required to describe a complex pattern on a microminiature semiconductor device. For example, when a 0.5 micrometer electron beam is utilized, one million bits of data are required to raster scan a pattern only 0.5 millimeter on a side. The data describing the pattern to be exposed is typically stored on magnetic tape or disk in the form of figure data, which specifies the location, size, and shape of the various features. In a raster scan system, conversion of figure data to a bit map image of the area to be exposed is required prior to writing of the pattern. The time required for conversion of figure data can be considerable.
In the exposure of 1X (actual size) masks or semiconductor wafers, the die pattern is repeated 25 to 100 times. Prior art systems have taken advantage of this repetition of patterns to reduce the total time spent in figure data conversion. Figure data for a stripe or a portion of a stripe is converted to a bit map once and then the corresponding stripe is exposed on each of the 25 to 100 die. Using this approach, the figure data conversion time is typically 10% to 25% of the total time to expose a workpiece.
It has become desirable to fabricate reticles using electron beam exposure systems. A reticle is a type of mask which is 5X (five times) or 10X (ten times) the actual device size and which contains one, or at most several, die, or repetitions of the pattern. The reticle is later used in a wafer stepper system to fabricate device layers in semiconductor wafers one or several die at a time. When an electron beam exposure system is used commercially for fabrication of reticles, an operating parameter of major importance is throughput in terms of reticles completed per unit time.
The lack of pattern repetition inherent in reticles causes an increase in time required for figure data conversion in prior art systems. Furthermore, the features on a 5X or 10X reticle are larger than the features on a 1X mask and require more bits in a bit map. Since the figure data is converted bit by bit, more time is spent in conversion of larger features. The overall effect is to drastically increase the figure data conversion time when prior art systems are used to fabricate reticles. Figure data conversion can take several times as long as actual writing time.
It is an object of the present invention to provide a pattern data handling system which provides high speed beam blanking data for an electron beam exposure system.
It is another object of the present invention to provide a pattern data handling system which can provide continuous beam blanking data for an electron beam exposure system.
It is yet another object of the present invention to provide a pattern data handling system for an electron beam exposure system wherein writing continues during bit map generation.
It is still another object of the present invention to provide a pattern data handling system for an electron beam exposure system wherein beam blanking data for reticles can be efficiently provided.